1. Field of the Invention
This invention relates to a nuclear magnetic resonance (NMR) apparatus used in the field for analyzing a sample of low concentration with the use of a superconducting magnet, and more specifically to a structure of a sensitive sample tube used in a nuclear magnetic resonance apparatus and a method for manufacturing the sample tube.
2. Brief Description of the Prior Art
In general, a nuclear magnetic resonance apparatus is required to use a sample tube having a thinnest possible wall thickness in order to make a sensitive measurement because a detector using the sample tube usually sets the outer diameter of the test tube to be very small such as, for example, 5 mm to 10 mm. Therefore, sample tubes, which are conventionally used as thin wall tube, are formed of a special hard glass material or the like with the wall thickness of the sample tubes as thin as 0.4 mm.
However, sample tubes with a further reduced wall thickness than mentioned above, such as the ultra thin wall, are fragile which makes it very difficult to use in comparison to a conventional thin wall tube. Therefore, even further reductions in the wall thickness of the ultra thin wall sample tubes is naturally limited. Also, the conventional ultra thin wall sample tube is made such that it has a uniform wall thickness over the entire body thereof, in order to obtain a sensitive measurement, in spite of the fact that a sample measurement by a nuclear magnetic resonance apparatus is actually carried out with respect to a very limited part (sample receiving chamber) in the vicinity of a bottom portion of the sample tube. This makes it even more difficult to make the sample tube, which is liable to break during the process of manufacture. Furthermore, since such sample tubes are manufactured on a small production basis by experienced and skilled workers, the production costs are prohibitively high. Moreover,the open ends of such sample tubes can easily break. Several times of use makes it practically impossible to use them even if handling is made with utmost care. In addition, it is difficult to cut such a thin tube, particularly at the opening area. Therefore, a specially-designed cutting machine is required. The need for the use of such a special cutting machine again results in increased production costs.
The present invention has been accomplished in view of the above.